Prevalence of SARS-COVID-19 serum IgG antibodies amongst staff on an acute surgical unit

Editor

Over 40,000 people have died in the UK from COVID-19, one of the highest pro rata death rates in the world¹. The pandemic has had a profound impact on the NHS and all health care systems around the world². Recently, SARS-CoV-2 antibody testing became more widely available for NHS employees and the wider healthcare community. It is believed that this scaled up testing will determine the rate of individual “immunity” and these data regarding antibody levels and the duration of protection, are essential for public health policy makers particularly if public health bodies are to adopt the concept of an “immune work cohort”³.

We present the results of SARS-CoV-2 antibody testing in healthcare staff from a tertiary acute general surgical unit that has been managing both acute surgical patients and elective cancer operations during the pandemic. We utilised the Public Health England approved Abbott ELISA based test⁴ which measures IgG antibodies. In our tertiary surgical unit between 29/03/2020 and 31/05/2020 we admitted 1964 patients with 71 testing positive for COVID-19. We surveyed 215 staff including a wide spectrum of healthcare workers from a variety of age ranges that had undergone antibody testing (Table 1). Interestingly, despite 175/215 reporting contact with COVID-19 positive patients only 6/215 had a positive PCR result and 15/215 reported a positive antibody test (Table 1). Only 3/6 individuals with a positive PCR test were demonstrated to have SARS-CoV-2-IgG antibodies. Additional data is needed on sero-conversion rates and immunity in healthcare workers, particularly in ethnic minority workers who make up a substantial proportion of the National Health Service workforce and who are at a higher risk from COVID-19.

Total Number of staff surveyed	N = 215	Positive antibody result N = 15	Staff members reporting having any contact with COVID-19 positive patients N = 175	Staff members reporting having any contact with COVID-19 positive staff members or relatives N = 103	Staff members reporting having any COVID-19 symptoms N = 43	Positive throat PCR test N = 6
Age Range
20-29	57	6	51	35	11	2
30-39	63	5	52	29	13	1
40-49	62	4	53	29	13	3
50-59	28		17	8	5
60-69	5		2	2	1
Job Position
Admin/Clerical	18	1	2	3	2
Consultant	10		10	4
Housekeeping/logistics	12	1	12	4
Junior Doctor	43	2	40	27	7	2
Nurse	84	10	69	45	26	4
Nursing-Assistant	35	1	30	18	6
Theatre Staff	13		12	2	1

Our “immunity” rate of 7%, although in line with a recently publish paper from Switzerland⁵, is extremely low and concerning especially in respect of the anticipated “herd immunity”. Herd immunity would mitigate many of the issues presently being confronted and it will clearly be many months at least before this makes a realistic contribution. A recent study of 105 anaesthesiologists and affiliated intensive care workers in New York found 54% reported exposure to COVID-19 patients with 26% reporting post-exposure symptoms⁶ and COVID-19 antibodies were detected in 12·1%. Our relatively low rate of positive antibodies can be attributed to the combination of early and rapid testing, isolation of emergency and elective patients, full availability and early implementation of personal protective equipment and a relative low incidence of COVID-19 in our community (2494 cases to 29/06/2020) and hospitals (1007 treated and discharged and 398 deaths (29/06/2020)). The recent spike in new cases in Leicester resulting in the first local lockdown in the UK will test this hypothesis and the ability of these hospital protocols to control our in-hospital nosocomial transmission.

The identification of COVID-19 positive patients and subsequent tracing must remain the priority and continued assessment of COVID-19 antibody prevalence will provide essential seroprevalence data that public health bodies need to inform their advice as the pandemic evolves.